The invention relates to a radiation-emitting semiconductor diode comprising a semiconductor body having a semiconductor substrate of a first conductivity type and consisting of gallium arsenide (GaAs), which is provided on the lower side with a conducting layer and on which are at least successively disposed a first cladding layer of the first conductivity type, an active layer, a second cladding layer of a second conductivity type opposite to the first conductivity type and a contact layer of the second conductivity type and consisting of gallium arsenide (GaAs), the semiconductor body comprising a mesa-shaped strip, which adjoins its surface, which at least comprises the contact layer and on which a conducting layer is disposed, which extends beyond the mesa-shaped strip and forms outside it with a semiconductor layer underlying the conducting layer a junction forming a barrier. The invention further relates to a method of manufacturing a radiation-emitting semiconductor diode, in which there are successively provided on a semiconductor substrate of gallium arsenide (GaAs) at least a first cladding layer of the first conductivity type, an active layer, a second cladding layer of the second conductivity type and a contact layer of the second conductivity type and consisting of gallium arsenide (GaAs), while by means of photolithography and etching a mesa-shaped strip is formed, which comprises at least the contact layer, after which a conducting layer is provided on the substrate and a conducting layer is provided over and outside the mesa-shaped strip, which forms outside the mesa-shaped strip with a semiconductor layer underlying the conducting layer a junction forming a barrier.
Such radiation-emitting diodes, more particularly when they are in the form of a laser, constitute radiation sources for inter alia data-processing systems, such as printers, by means of which information is written, and such as "optical disk" systems, in which information is read out --for example so-called compact disc (CD) players and Video Long-Play (VLP) systems--or is written and read out--for example Digital Optical Recording (DOR). Also when such diodes are in the form of LED's, there are numerous applications in optoelectronic systems.
Such a radiation-emitting diode and such a method of manufacturing it, are known from the article by M. C. Amann, "New stripe-geometry laser with simplified fabrication process", which is published in Electron Lett., Vol. 15, No. 14, Jul. 5, 1979, pp. 441-442. In this article, a radiation-emitting semiconductor diode is described, in which are disposed on an n-type GaAs substrate an n-type AlGaAs cladding layer, a GaAs active layer, a p-type AlGaAs cladding layer and a p-type GaAs contact layer. Both the substrate and the contact layer are provided with a conductive layer. The radiation-emitting diode comprises a mesa-shaped strip, which comprises at least the GaAs contact layer, which is etched away outside it, as a result of which at these areas a junction constituting a barrier is formed between the upper conductive layer and the second cladding layer. The radiation-emitting diode comprises a strip-shaped region, of which the mesa-shaped strip forms part, within which electromagnetic radiation can be produced by a present pn junction upon current passage in the forward direction. Due to the presence of the junction constituting a barrier, the current is mainly limited during operation to the mesa-shaped strip.
A disadvantage of the known semiconductor diode is that the properties of the junction constituting a barrier cannot be adjusted independently of, for example, the properties of the cladding layer. The disadvantage therefore resides in the fact that the properties of the cladding layer should be at the same time optimal for fulfilling various functions. In fact, the cladding layer fulfills several functions: optical and electrical enclosure of photons and charge carriers, respectively, in the active layer, current passage layer and barrier former. In the known method, moreover, a further disadvantage is obtained if the mesa-shaped strip also should comprise a part of the cladding layer in order to obtain so-called index guiding. In this case, the second cladding layer should be etched back to a small thickness outside the mesa-shaped strip, which process can be controlled only with difficulty. Moreover, if the thickness of the second cladding layer is not constant over the surface of a substrate, which in practice--especially when large substrates are used--is mostly the case, the etching process will result in a comparatively large spread in the thickness of the second cladding layer outside the mesa-shaped strip. As a result, radiation-emitting diodes are obtained having different properties, for example different degrees of index guiding, which is undesirable. A great disadvantage of the known semiconductor diode is--as already stated above--that the properties of the cladding layer should at the same time be optimal for fulfilling various functions.